Linux Babe published a guide about setting up a local DNS resolver on Ubuntu 20.04 LTS with BIND9.
Set Up Local DNS Resolver on Ubuntu 20.04 with BIND9
This tutorial shows you how to set up a local DNS resolver on Ubuntu 20.04, with the widely-used BIND9 DNS software. Why Run Your Own Local DNS Resolver?
Set Up Local DNS Resolver on Ubuntu 20.04 with BIND9 - LinuxBabe